wdiff draft-ietf-6man-oversized-header-chain-01.txt draft-ietf-6man-oversized-header-chain-02.txt

IPv6 maintenance Working Group (6man) F. Gont
Internet-Draft SI6 Networks / UTN-FRH
Updates: 2460 (if approved) V. Manral
Intended status: Standards Track Hewlett-Packard Corp.
Expires: January 17, May 9, 2013 July 16, November 5, 2012

Security and Interoperability Implications of Oversized IPv6 Header
Chains
draft-ietf-6man-oversized-header-chain-01
draft-ietf-6man-oversized-header-chain-02

Abstract

The IPv6 specification allows IPv6 header chains of an arbitrary
size. The specification also allows options which can in turn extend
each of the headers. In those scenarios in which the IPv6 header
chain or options are unusually long and packets are fragmented, or
scenarios in which the fragment size is very small, the first
fragment of a packet may fail to include the entire IPv6 header
chain. This document discusses the interoperability and security
problems of such traffic, and updates RFC 2460 such that the first
fragment of a packet is required to contain the entire IPv6 header
chain.

Status of this Memo

This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on January 17, May 9, 2013.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Interoperability Implications of Oversized IPv6 Header
Chains . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Forwarding Implications of Oversized IPv6 Header Chains . . . 6
5. Security Implications of Oversized IPv6 Header Chains . . . . 7
6. Updating RFC 2460 . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

1. Introduction

[RFC2460] allows for an

With IPv6, IPv6 header chain options are carried inside one or more IPv6 Extension
Headers [RFC2460]. A sequence of more than one IPv6 Extension
Headers in a row is commonly called an arbitrary size. It
also allows the headers themselves to have options, which can change
the size of the headers. "IPv6 Header Chain". In those
scenarios in which the IPv6 header chain is unusually long and
packets are fragmented, or scenarios in which the fragment size is
very small, the first fragment of a packet may fail to include the
entire IPv6 header chain.

While IPv4 had a fixed maximum length for the set of all IPv4 options
present in a single IPv4 packet, IPv6 does not have any equivalent
maximum limit at present. This document
discusses updates the interoperability and security problems set of such traffic, IPv6
specifications to create an overall limit on the size of the
combination of IPv6 options and IPv6 Extension Headers that is
allowed in a single IPv6 packet. Namely, it updates RFC 2460 such
that the first fragment of a fragmented datagram is required to
contain the entire IPv6 header chain.

It should be noted that this requirement does not preclude the use of
e.g. IPv6 jumbo payloads but instead merely requires that all
*headers*, starting from IPv6 base header and continuing up to the
upper layer header (e.g. TCP or the like) be present in the first
fragment.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. Terminology

IPv6 Extension Headers:
Any Extension Headers as described in Section 4 of [RFC2460], and
specified in [RFC2460] or any subsequent documents.

Entire IPv6 header chain:
All protocol headers starting from the fixed IPv6 header till up to
(and including) the upper layer protocol header (TCP, UDP, etc. --
assuming there is one of those), including any intermediate IPv6
extension headers.

Note: If there is an upper layer header, only the header (and
not its payload) are considered part of the "entire IPv6 header
chain". For example, if the upper layer protocol is TCP, only
the TCP header (and not its possible data bytes) should be
considered part of the "entire IPv6 header chain".

3. Interoperability Implications of Oversized IPv6 Header Chains

Some transition technologies, such as NAT64 [RFC6146], may might need to
have access to the entire IPv6 header chain in order to associate an
incoming IPv6 packet with an ongoing "session".

For instance, Section 3.4 of [RFC6146] states that "The NAT64 MAY
require that the UDP, TCP, or ICMP header be completely contained
within the fragment that contains fragment offset equal to zero".

Failure to include the entire IPv6 header chain in the first-fragment
may
might cause the translation function to fail, with the corresponding
packets being dropped.

4. Forwarding Implications of Oversized IPv6 Header Chains

A lot of the switches and Routers in the internet do hardware based
forwarding. To be able to achieve a level of throughput, there is a
fixed maximum number of clock cycles dedicated to each packet.
However with the use of unlimited options and header interleaving,
larger packets with a lot of interleaving might have to be forwarded
to the software. It This is for this one reason that why the maximum size of valid
packets with interleaved headers needs to be limited.

5. Security Implications of Oversized IPv6 Header Chains

Most firewalls enforce they their filtering policy based on the following
parameters:

o Source IP address

o Destination IP address

o Protocol type (e.g. ICMPv6, TCP, UDP, SCTP)

o Transport-layer Source port Port number

o Transport-layer Destination port Port number

Some firewalls reassemble fragmented packets before applying a
filtering policy, and thus always have the aforementioned information
available when deciding whether to allow or block a packet. However,
other stateless firewalls (generally prevalent on small/ home office
equipment) do not reassemble fragmented traffic, and hence have to
enforce their filtering policy based on the information contained in
the received fragment, as opposed to the information contained in the
reassembled datagram.

When presented with fragmented traffic, many of such firewalls
typically enforce their policy only on the first fragment of a
packet, based on the assumption that if the first fragment is
dropped, reassembly of the corresponding datagram will fail, and thus
such datagram will be effectively blocked. However, if the first
fragment fails to include the entire IPv6 header chain, they may might
have no option alternative other than "blindly" allowing or blocking the
corresponding fragment. If they blindly allow the packet, then the
firewall can be easily circumvented by intentionally sending
fragmented packets that fail to include the entire IPv6 header chain
in the first fragment. On the other hand, first-fragments that fail
to include the entire IPv6 header chain have never been formally
deprecated and thus, in theory, might be legitimately generated.

6. Updating RFC 2460

If a an IPv6 packet is fragmented, the first fragment of the that IPv6
packet (i.e.,
that with the fragment having a Fragment Offset of 0) MUST
contain the entire IPv6 header chain.

7. IANA Considerations

There are no IANA registries within

A host that receives an IPv6 first-fragment that does not contain the
entire IPv6 header chain SHOULD drop that packet, and also MAY send
an ICMPv6 error message to the (claimed) source address (subject to
the sending rules for ICMPv6 errors specified in [RFC4443]).

An intermediate system (e.g. router, firewall) that receives an IPv6
first-fragment that does not contain the entire IPv6 header chain MAY
drop that packet, and MAY send an ICMPv6 error message to the
(claimed) source address (subject to the sending rules for ICMPv6
error messages specified in [RFC4443]). Intermediate systems having
this document. The RFC-Editor
can remove capability SHOULD support configuration (e.g. enable/disable) of
whether such packets are dropped or not by the intermediate system.

If a host or intermediate system drops an IPv6 first-fragment because
it does not contain the entire IPv6 Header Chain, and sends an ICMPv6
error message due to that packet drop, then the ICMPv6 error message
MUST be Type 4 ("Parameter Problem") and MUST use Code 3 ("First-
fragment has incomplete IPv6 Header Chain").

Implementations SHOULD support configuration of whether an ICMPv6
error/diagnostic message is sent when such packet drops occur.
Implementations might consider providing not only an enable/disable
configuration, but also other settings (e.g. rate-limit the sending
of this section before publication kind of ICMPv6 error message).

Sending this document as ICMPv6 error message when such packets are dropped can
be very helpful in diagnosing operational IPv6 network problems, for
example if recursive tunnels or certain link technologies have
reduced the end-to-end MTU from larger more common values. However,
such ICMPv6 messages also might be operationally problematic, for
example if an
RFC. adversary forges the source address on IPv6 first-
fragment packets that do NOT contain the entire IPv6 Header Chain.
So configurability about sending these ICMPv6 error messages is very
important to network operators for this situation.

7. IANA Considerations

IANA is requested that the "Reason Code" registry for ICMPv6 "Type 4
- Parameter Problem" messages be updated as follows:

CODE NAME/DESCRIPTION
3 IPv6 first-fragment has incomplete IPv6 header chain

8. Security Considerations

This document describes the interoperability and security
implications of IPv6 packets or first-fragments that fail to include
the entire IPv6 header chain. The security implications include the
possibility of an attacker evading network security controls such as
firewalls and Network Intrusion Detection Systems (NIDS) [CPNI-IPv6].

This document updates RFC 2460 such that those packets are forbidden,
thus preventing the aforementioned issues.

This specification allows nodes that drop the aforementioned packets
to signal such packet drops with ICMPv6 "Parameter Problem, IPv6
first-fragment has incomplete IPv6 header chain" (Type 4, Code 3)
error messages.

As with all ICMPv6 error/diagnostic messages, deploying Source
Address Forgery Prevention filters helps reduce the chances of an
attacker successfully performing a reflection attack by sending
forged illegal packets with the victim/target's IPv6 address as the
IPv6 Source Address of the illegal packet [RFC2827] [RFC3704].

9. Acknowledgements

The authors of this document would like to thank Ran Atkinson for
contributing text and ideas that were incorporated into this
document.

The authors would like to thank (in alphabetical order) Ran Atkinson,
Fred Baker, Dominik Elsbroek, Bill Jouris, Suresh Krishnan, and Dave Thaler
Thaler, and Eric Vyncke, for providing valuable comments on earlier
versions of this document.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.

[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.

10.2. Informative References

[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.

[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.

[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.

[CPNI-IPv6]
Gont, F., "Security Assessment of the Internet Protocol
version 6 (IPv6)", UK Centre for the Protection of
National Infrastructure, (available on request).

Authors' Addresses

Fernando Gont
SI6 Networks / UTN-FRH
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina

Phone: +54 11 4650 8472
Email: fgont@si6networks.com
URI: http://www.si6networks.com

Vishwas Manral
Hewlett-Packard Corp.
191111 Pruneridge Ave.
Cupertino, CA 95014
US

Phone: 408-447-1497
Email: vishwas.manral@hp.com
URI: